In principle, switches in motor vehicle seat belt buckles serve to recognize a belt tongue locked in the belt buckle. If an occupant is recognized as occupying the vehicle seat via a suitable sensor device, but no signal representing a locked belt tongue is generated by the switch, then, for example, an optical and/or acoustic signal can be generated, which is only switched off if the occupant has buckled up, i.e., if a belt tongue is locked in the belt buckle. Furthermore, the signal can also be used to provide that in the case of an accident certain additional restraining devices, such as, for example, airbag devices, are not activated or only activated if a locked belt tongue has been recognized, i.e., if the switch has generated a signal.
Possible embodiment of such switches include contactless Hall sensors, which, however, are susceptible and proper operation in response to external magnetic fields.
Furthermore, the use of mechanical switches is known, for example, from EP 1 485 276 B1 or DE 10 2012 208 779 A1. In these switches, two electrically conductive contact elements are provided which are part of an electrical circuit. One of the contact elements is configured as a contact spring and protrudes with a section in an insertion channel in which an ejector of the belt buckle is pushed during the locking movement of the belt tongue. Due to the insertion of the ejector it reaches direct abutment on the contact spring so that the contact spring is compelled into a movement whereby the contact of the contact elements is opened or closed. Due to the opening or the closing of the contact, a signal is generated which is representative of the belt tongue locked in the belt buckle. Depending on whether the signal is generated by closing or opening of the contact of the contact elements, the switch is also referred to as closer or opener. So that the contact is securely opened or closed, the contact spring projects at least with a section in the insertion channel, while the contact point is disposed in a protected cavity outside the insertion channel. The contact spring must therefore have a complex geometry so that the inserted part inevitably comes into abutment on the contact spring in any event, and the contact spring is correspondingly moved during the further insertion movement for opening or closing of the contact.
The functionality of the switch thus depends on the compliance of the complex geometry of the contact spring, which can be changed, for example, by the continuous load of a plurality of actuation cycles. Furthermore, the contact spring must be configured to be abrasion-resistant and have sufficient flexural strength for a very high number of insertion operations of the belt buckle so that the signal is generated in a functionally secure manner even after a long service life of the belt buckle. In addition the contact spring, as part of the contact, must of course also fulfill the requirements with respect to electrical conductivity.
Furthermore a belt buckle is known from U.S. Pat. No. 3,956,603 wherein the contact pairing with a contact spring and a fixed contact is disposed outside the insertion channel, while the movement of the contact spring is compelled by a coupling member projecting into the insertion channel. The pivotable coupling member projects with a first section into the insertion channel, and is shaped and supported such that it is pivoted by the inserted belt tongue during the insertion movement and comes into abutment on the contact spring via a second section. During the further insertion movement of the belt tongue, the coupling member is further pivoted, whereby the contact spring performs a movement with respect to the fixed contact and the contact is opened. The contact member is supported here via an additional spring on the housing of the switch so that it is urged in a spring-loaded manner into a position wherein it engages in the insertion channel via the first section. The advantage of this solution can be seen in that the contact spring no longer itself engages in the insertion channel, and the opening movement of the contact spring is coupled by the coupling member whose movement is itself compelled in turn by the inserted belt tongue. The ejector or the belt tongue thus abut on the coupling member instead of on the contact spring; the coupling member transfers the movement. Overall the contact spring can thereby be preserved. In addition, the contact spring can thereby have a much simpler geometry so that it is simpler to manufacture and its function in particular is no longer dependent on the compliance with the complex geometry. Furthermore, the contact spring can be designed more simply and more functionally secure for the required flexural strength.
The object of the present invention is to provide a cost-effectively manufactured switch for a belt buckle of a seatbelt device with a further-improved functional security.